This invention relates to a method of operating a telecommunications system comprising a switching facility and subscriber channels over which data are transmissible in packet form.
Such a telecommunications system is, for example, an ISDN system, which transmits both voice and data in digital form from one subscriber over 64-kb/s channels, called xe2x80x9cB channelsxe2x80x9d, to another subscriber.
The invention is applicable to the transmission of data of the subscriber if these data are offered in packet form, i.e., as a sequence of packets, on the subscriber""s access channel (B channel). As is well known, these packets include destination address information of a general kind (i.e., not necessarily the telephone number of the desired subscriber).
The invention is applicable to voice transmission if the subscriber terminal itself converts voice information into packet form, as is done for voice transmission over the Internet.
Prior-art telecommunications systems with a switching facility are normally dimensioned so that not all subscribers can establish a call to the switching facility and to other subscribers at the same time, but the capacity of the switching facility in terms of channels that can be switched simultaneously is less than the number of subscribers connected. During data transmission, particularly if the duration of the respective data call is long compared to the duration of usual telephone calls, this may result in access to the switching facility being temporarily impossible because all channels leading to the switching network of the switching facility or all outgoing channels are busy.
The invention has for its object to provide a possibility of diminishing this disadvantage.
This and other objects are achieved by a method of operating a telecommunications system, which includes a switching facility and a plurality of subscriber channels over which data are transmitted in packet form, wherein calls from subscribers to an internet are recognized, and wherein, at the front end of the switching facility associated with the subscribers, those packets of the plurality of subscriber channels that are to be sent to the internet are combined onto a single channel.
Accordingly, the access channels (B channels) of two or more subscribers establishing a call to the same destination unit, for example to an Internet service provider, are no longer switched individually and separately up to the destination unit, but the packets transmitted on these channels are received already in the line circuit area of the switching facility by a concentrator and transmitted over one or a small number of outgoing channels to the destination unit.
An important advantage accrues from the fact that the packets of two or more subscribers are switched through in the switching facility by a single switching path, in contrast to the prior-art method where during data transmission a separate switching path was needed for the B channel of each subscriber, as is also the case for the through-switching of telephone calls.
The invention also provides a telecommunications system having subscriber channels over which data are transmitted in packet form, and a switching facility having crosspoints, wherein each crosspoint is capable of switching one of the subscriber channels to an outgoing channel. Further, at least one concentrator is provided, which combines packets of two or more subscriber channels that are to be sent to the internet onto at least one concentrating channel that leads to the switching facility. Therein, the concentrator is switched via a switching path and the number of concentrating channels is less than the number of subscriber channels.
According to another formulation of the claimed invention, a concentrator is provided, which has at least one device for concentrating data incoming on two or more B channels in a single, outgoing channel.
If the invention is implemented in an ISDN switching facility, where each subscriber channel has a capacity of 64 kb/s, in one embodiment of the invention the packets of different subscribers are transferred into a transmission buffer according to their temporal arrival at the concentrator, and subsequently transmitted in mixed form and in close succession on the transmission channel of likewise 64 kb/s to the common destination unit. This channel then requires essentially only that technical equipment in the switching facility necessary for a single telephone call, referred to in the following as a single switching path.
How many subscriber channels can be concentrated in one outgoing channel depends on the type of the application and the resulting average data volume per subscriber channel and unit of time. In this respect, the invention can be dimensioned very differently.
In the case of Internet access, empirical values show that on an average, a subscriber uses only about 10-15 percent of the maximum transmission capacity of 65 kb/s over the total call duration. Accordingly, the packets of eight subscriber channels, for example, could be combined at the concentrator onto one channel to the destination unit. To be able to handle short-time peak traffic, however, the concentration factor will have to be only about 3:1 if only a single outgoing channel is present.
Therefore, to increase the efficiency of the concentrator, instead of switching only one transmission channel to the destination unit, each concentrator switches a small group of such channels, over which the packets of 16 active subscriber channels, for example, are then transmitted simultaneously. This suffices to provide access to the concentrator for 64 ISDN subscribers.
An important feature of one embodiment of the invention is that in such a major ISDN line circuit area, which typically consists of eight line modules each having eight ISDN basic-access arrangements with two B channels each (i.e., a total of 128 B channels), the concentrator is dispersed over all (up to eight) modules involved, which contain one control computer each. The purpose of the arrangement is that access can be gained from any of the line modules to any of the established concentrating channels to the destination unit. Prior to each transmission of a packet, a fast access logic in the hardware of each module detects traffic pauses in the individual concentrating channels, and the packet is then transmitted over a currently idle concentrating channel. Contention is resolved quickly by the access logics of all affected line modules agreeing automatically on a uniform channel allocation. It is also possible to use other known methods of resolving such conflicts.
In a simple embodiment of the invention, prior to the beginning of its use, each of the concentrating channels between the concentrator and the destination unit is switched through the switching facility as a semi-permanent connection, and is then available to the concentrator for an essentially unlimited period of time.
In a more sophisticated embodiment of the invention, the number of concentrating channels can be automatically increased or reduced from the concentrator depending on the traffic volume, with the method used in the switching facility for switching these channels being the same as that used for switching voice channels. According to another feature of the invention, if required, two or more destination units are reachable from a concentrator; then at least one concentrating channel has to be switched to each destination unit. In that case, the concentrator, when transmitting the packets, sees to it that according to the address information contained in the header of each packet, only those concentrating channels that lead to the addressed destination unit are used for the transmission of this packet.
The determination that access to the Internet is desired is derived from the dialling information entered by the subscriber. This may be, for example, the telephone number of a service provider, a group of digits in the telephone number assigned to two or more service providers, or a special prefix.
So far, only those data were considered that are sent from a subscriber toward, e.g., the Internet. However, the various parts of the switching facility and the concentrator are advantageously designed to also supply data flowing in the opposite direction to the respective subscriber, as is also the case if each subscriber is assigned a separate subscriber channel for data transmission in the conventional manner.